Growth factors (or neurotrophic factors) promote the differentiation, growth and survival of numerous peripheral and central nervous system neurons during development and adulthood. The molecular characteristics; regulation and signal transduction mechanism for a number of neurotrophic factors have been identified. The most therapeutically promising of these molecules are nerve growth factor (NGF), brain-derived neurotrophic factor (BNDF), ciliary neurotrophic factor (CNTF), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), and glial cell-line derived neurotrophic factor (GDNF).
Available data suggests that neurotrophic factors will be useful in the treatment of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Additionally neurotrophic factors have shown beneficial effects in animal models of peripheral nerve damage and toxin induced neuropathy [CNS Drugs 1994 2 (6) 465-478].
Various rat studies predict that compounds mimicking or enhancing the function of NGF can rescue septal cholinergic neurons and alleviate benign forgetfulness and the memory impairment seen in senile dementia [Science 1994 264 772-774].
Recent studies have shown that NGF has a neuro protective effect on hippocampal neurons after cerebral ischaemia, which predicts a potential therapeutic role for NGF in the treatment of cerebral ischaemic neuronal damage [NeuroReport 1995 6 (4) 669-672].
Growth factors initiate their biological action by binding to specific cell surface receptors. Binding of the growth factor to its receptor activates the intracellular signal transduction, leading to the generation of various second messengers and activation of enzyme cascades, involving tyrosine kinases and protein kinase C, and culminates in a biological effect. The intracellular signal transduction pathway is not yet fully understood.
NGF and related neurotrophins are large peptides, which makes them unlikely therapeutic candidates. Poor pharmacokinetic parameters (e.g. poor oral absorption and short in vivo half life), and administration to the target organs represent the major problems.
There is a continued need for the development of new compounds capable of interacting with the neurotrophin-receptors, and which shows physicochemical properties different from the neurotrophins.